1. Field of Invention
The present invention relates to a converter and, more particularly, to a dual-source converter that can be switched between a single-source mode and a dual-source mode.
2. Related Prior Art
As the population of the world is growing, the consumption of energy is increasing while the reserve of non-renewable energy is declining. Hence, It is getting more important to use renewable energy. To use various types of the renewable energy, there are various types of devices such as fuel cells, solar cells and wind turbines. With help from power electronics and automation techniques, these devices can be used in vehicles, uninterruptible power supplies and independent generators for example. The fuel cells, solar cells and wind turbines however generate current at low voltage. Moreover, the voltage of the current fluctuates with load or the power production is limited by the natural environment. Generally speaking, the renewable energy cannot be sued in ordinary electric appliances directly. Therefore, DC/DC converters are necessary electric devices for using the renewable energy.
Conventionally, one set of electric devices for using the renewable energy is used together with one set of converters to convert the various types of the renewable energy. A conventional system includes many converters connected in parallel to a DC high-voltage bus, and is used as a power source in front of an inverter or used as a direct power source for an electric appliance. The conventional system is however bulky, complicated and expensive. Most of the DC/DC converters are conventional boost-type DC/DC converters. By adjusting the duty cycle of a switch, the boost ratio is controlled. There is however a problem with this process. Conventionally, the switching of the switch is hard switching, and there is a reverse recovery current in an output diode. In the transient on state of a power semiconductor switch, a huge current travels through the output diode to build a reverse-biased voltage. However, the large current, which travels through the semiconductor switch, incurs a serious loss in the switching and a low conversion efficiency.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.